The present invention is directed to electric motor drive controllers in general, and more particularly, to an electric motor drive controller comprising a voltage control circuit operative in different operating modes for generating different voltages for a drive signal to control a motor of an electric vehicle powered by an energy source.
A typical electric vehicle draws the energy from an energy storage device such as a battery, sometimes supported by secondary energy sources. The power is processed in a drive power control which controls the voltages and currents which are fed into one to several electric motors. In general, for slow or small scale electric vehicles, such as wheelchairs, bicycles or transportation systems permanent magnet motors are used, i.e. DC, AC or multiphase machines with permanent excitation.
Extending the operating range of motors with permanent excitation generally requires enhancing the voltage and/or current capabilities of a drive power controller. The limited dynamic range of the power controller restricts the system to a certain operating range. As the relationship between current and torque, as well as between voltage and speed is fixed, the controller has to deliver very high currents for high torque output, and very high voltages to achieve high speeds.
A common solution is using motors with a separately adjustable field excitation instead of the permanent excitation. This solution allows additional influence by determining the relationship between voltage and speed (the Ke-Factor), and current and torque. With strong excitation high torque at low currents can be achieved, with weak excitation the motor runs fast at a relatively low voltage in the other winding. Suitable motors consist of an additional armature winding which requires the use of additional slip rings. The drive power controller has to offer additional circuitry to support the additional winding. Another approach is adding a gearbox, or a variable transmission between motor and wheel. For cost reasons these approaches are only applicable to large scale vehicles, or in special circumstances.
An approach related to motors with permanent excitation is a permanent increase of the power supply voltage, for example by increasing the number of battery cells. At given dimensions, this requires reducing the size of the individual cells, increasing the power supply""s impedance. At the same time, the motors can take more stall current because of the higher voltage. The system""s efficiency would decrease significantly, and special precautions against overload may be required. Further, the effective resolution in terms of Volts/bit rises proportionally, i.e. the voltage steps will become larger. As one consequence, the motors start to run roughly.
The present invention provides a solution which overcomes the drawbacks of the aforementioned solutions to increase the maximum vehicle speed, while fully maintaining the other key parameters.
In accordance with one aspect of the present invention, an electric motor drive controller for an electric vehicle driven by a motor with permanent excitation and powered by an energy source comprises: a power control stage coupleable to the motor for generating a drive signal at a voltage to control the motor at a desired speed; a voltage control circuit connectable between the energy source and the power control stage for controlling the voltage of the drive signal at a first voltage potential in one operating mode and at a voltage potential greater than the first voltage potential in another operating mode; and a mode controller for controlling the operating modes of the voltage control circuit based on properties of the drive signal.
In accordance with another aspect of the present invention, a motor drive control system for an electric vehicle driven by an electric motor powered by an energy source comprises: a power control stage coupleable to the motor for generating a drive signal at a voltage to control the motor at a desired speed; a first motor drive controller connectable between the energy source and the power control stage for controlling the voltage of the drive signal at a first voltage potential, the first motor drive controller operative to monitor the properties of the drive signal; and a second motor drive controller connectable between the energy source and the power control stage for controlling the voltage of the drive signal at a second voltage potential in one operating mode and at a voltage potential greater than the second voltage potential in another operating mode, the second motor drive controller including a mode controller for communicating with the first motor drive controller to determine the properties of the drive signal and for controlling the operating modes of the second motor drive controller based on the communicated properties of the drive signal.
In accordance with yet another aspect of the present invention, a motor drive control system for an electric vehicle driven by an electric motor powered by an energy source comprises: a power control stage coupleable to the motor for generating a drive signal at a voltage to control the motor at a desired speed; a first motor drive controller connectable between the energy source and the power control stage for controlling the voltage of the drive signal at a first voltage potential; a second motor drive controller connected, when activated, between the energy source and the power control stage for controlling the voltage of the drive signal at a second voltage potential in one operating mode and at a voltage potential greater than the second voltage potential in another operating mode, the second motor drive controller including a mode controller for controlling the operating modes of the second motor drive controller; and the first motor drive controller including means for monitoring the activation status of the second motor drive controller; and means governed by the monitoring means for connecting the first motor drive controller between the energy source and the power control stage based on the monitored activation status of the second motor drive controller.